1. Technical Field
The present disclosure relates to an electrolytic capacitor and a method for manufacturing the electrolytic capacitor, and electrode foil used for an electrode of an electrolytic capacitor or the like and a method for manufacturing the electrode foil.
2. Background Art
With achieving of a high frequency of electronic devices, also in an electrolytic capacitor that is one of electronic components, a large-capacitance electrolytic capacitor that is more excellent in an impedance characteristic in a high frequency region than a conventional electrolytic capacitor is demanded. In order to respond to such a demand, various solid electrolytic capacitors in which a conductive polymer having high electrical conductivity is used as a solid electrolyte is studied.
Such solid electrolytic capacitors are widely employed in a power supply circuit of a personal computer and the like because they have a particularly excellent high frequency characteristic in addition to a life and a temperature characteristic.
In a conventional solid electrolytic capacitor in which aluminum foil is used as an electrode, a dielectric layer of an aluminum oxide film is artificially formed by chemical conversion treatment on a surface of aluminum foil that becomes an anode. On the other hand, aluminum foil that becomes a cathode is not subjected to chemical conversion treatment, and therefore an aluminum oxide film that is artificially formed does not exist on a surface of this aluminum foil. However, the aluminum oxide film actually exits also on the surface of the aluminum foil that becomes the cathode by natural oxidation that occurs from a time when the aluminum foil is manufactured to a time when the aluminum foil is used as the electrode of the solid electrolytic capacitor.
In this case, as a whole of the solid electrolytic capacitor, a layer structure is formed as following; (1) aluminum foil that becomes an anode, (2) an aluminum oxide film formed on a surface of the aluminum foil that becomes the anode, (3) a conductive polymer layer, (4) a film of naturally oxidized aluminum that exists on a surface of aluminum foil that becomes a cathode, and (5) the aluminum foil that becomes the cathode. As a result, the aluminum oxide film that exists on the surface of the aluminum foil that becomes the cathode becomes a dielectric layer, as well as the aluminum oxide film formed on the surface of the aluminum foil that becomes the anode. That is, from a viewpoint of an equivalent circuit, two capacitors are connected in series, and therefore capacitance of a whole of the solid electrolytic capacitor is reduced.
In order to cope with such a problem, cathode foil is disclosed as a method for preventing a capacitance component from generating in the cathode. The cathode foil is obtained by formation of a chemical conversion coating film on the surface of the aluminum foil that becomes the cathode, and further formation of a film of metal nitride such as TiN or a film of metal oxide such as TiO on the chemical conversion coating film by a vapor deposition.